High-wear-resistant composite seal and method of making the same

ABSTRACT

A base metal, such as the aluminum or iron housing of a conventional rotary or reciprocating-piston internal combustion engine, and a sealing member applicable to the pistons or rotor thereof are coated with a layer of a wear-resistant alloy, such as molybdenum-ruthenium or tungsten-ruthenium alloy, either by evaporating the elements of the alloy be electron guns onto the surfaces to be coated or by vaporizing a wire of the same alloy in a vacuum chamber by the application of a high-tension electrical discharge through the wire from an electrical condenser bank. Depositing the alloy is done on a production basis by passing workpiece holders in a circular path through a vacuum chamber beneath the electron guns, followed by a realloying step through a laser beam, an acid dip, a rinsing dip, a drying by heat, and a final honing.

BACKGROUND OF THE INVENTION

A critical problem in the rotary internal combustion engine known as theWankel engine, has been the provision of a sufficiently gas-tight anddurable seal between the housing stator and the lobes of the rotor. Thelack of a sufficiently durable seal has greatly retarded theintroduction of such high-speed engines of medium and large chambercapacity and power. Such engines hitherto attemptedly produced haverapidly destroyed their seals so that leakage soon occurs between thestator and rotor surfaces with the result that the engine has quicklylost power and has become unacceptable to purchasers and unreliable inoperating life.

SUMMARY OF THE INVENTION

The wear surfaces of the improved composite seals for the stator androtor are coated with an extremely high wear-resistant alloy, such asmolybdenum-ruthenium or tungsten-ruthenium, thereby enormouslylengthening the working life of the engine by the extremely highwear-resistant properties of the said seal-coating alloys.

In the drawings,

FIG. 1 is a side elevation of a high wear-resistant composite rotorseal, according to the invention;

FIG. 2 is an enlarged cross-section taken along the line 2--2 in FIG. 1

FIG. 3 is a diagrammatic top plan view of a first form of apparatus forapplying the high wear-resistant sealing coating to the base portion ofthe composite rotor seal of FIGS. 1 and 2;

FIG. 4 is a diagrammatic vertical section, upon an enlarged scale, takenalong the line 4--4 in FIG. 3;

FIG. 5 is a diagrammatic side elevation, with portions broken away, of adevice for vaporizing a wire of high wear-resistant alloy and applyingthe vapor as a coating upon the interior of multiple internal combustionengine stators for use with the rotors equipped with the rotor seal ofFIGS. 1 and 2;

FIG. 6 is a cross-section along the line 6--6 in FIG. 5, through one ofthe internal combustion engine stators of the bank thereof beinginternally coated in FIG. 5;

FIG. 7 is a diagrammatic side elevation of a high-tension electricalenergization circuit employed with the vaporization device of FIG. 5;and

FIG. 8 is a diagrammatic central vertical section, upon a reduced scale,through a simplified device for vaporizing a wire of high wear-resistantalloy and applying the vapor as a coating upon a collection of the sealsshown in FIG. 1.

Referring to the drawings in detail, FIG. 1 shows a high wear-resistantcomposite rotor seal, generally designated 14, as consisting generallyof a base 16 and a wear-resistant coating 18. The base 16 is in the formof an elongated twin-legged bar which is particularly well adapted formounting on the tips of the lobes of the rotor of a conventional rotaryinternal combustion engine (not shown) of the so-called Wankel typehaving a roughly triangular rotor, the lobes of which rotate in anorbital path relatively to the constricted passageway between theopposite end portions of a roughly Figure 8-shaped chamber. For thispurpose, the base 16 is of elongated shape in the form of a bar having astraight upper surface 20 corresponding to the axial length of the lobeof the rotor upon which it is mounted and having an arcuateconfiguration in cross-section which has a top portion 22 of longerradius of curvature than the opposite side portions 24 and meeting thelatter at opposite junction lines 26 (FIG. 2). The base 16 of the rotorseal 14 has a bottom surface 28 which includes a straight intermediateportion 30 terminating in downwardly-extending leg portions 32 withlower ends 34 from which outer notched portions 36 joinupwardly-inclined surfaces 38 terminating in opposite ends 40. Theintermediate bottom portion 30 and the inner surfaces 42 of the legportions 32 form an indentation 44. The thickness of the coating 18 inFIG. 2 is exaggerated in order to render it visible. The base 16preferably has parallel opposite sides 46 (FIG. 2) which cooperate withthe bottom surfaces 34 to form rectangular portions 48 which fit intocorresponding paraxial (not shown) recesses in the tips of the threelobes of the engine.

The bar seal coating machine, generally designated 50, shown in FIG. 3produces the composite bar seal 10 of FIGS. 1 and 2 on a continuousproduction basis by the evaporating method using conventional electrongun procedure. It consists of a turntable 52 mounted for rotation abouta central axis 54 and having multiple magnetic work holders 56 anddisposed at stations numbered sequentially 1 to 12 inclusive in FIG. 3.The work holders 56 are filled with uncoated seal bases 16 mounted withtheir legs 32 resing upon the top surface 58 at the loading station 60with their upper surfaces 20 facing upward (FIG. 2). The turntable 52 isthen rotated step-by-step in a clockwise direction with a dwell at eachstation, as the processing is carried out in a manner described below.The mounting and rotation of the turntable 52 are conventional andwell-known in the welding industry and their details are beyond thescope of the present invention. Such a turntable installation forelectron beam welding purposes, for example, is manufactured and sold bySciaky Brothers, Inc., of Chicago, Ill.

Mounted adjacent the periphery of the turntable 52 at one side thereof(FIG. 4) is a platform 62 upon which is arranged an electron-gun coatingunit, generally designated 64. The unit 64 includes an outer housing 66and an inner housing 68 between which is an outer low-vacuum chamber 70,whereas the inner housing 68 contains an inner high-vacuum chamber 72.The platform 62 has an outwardly-extending wall 74 adjacent theperipheral portion 76 of the upper surface 82 of the turntable 52 andthe low-vacuum space 78 between the wall 74 and said peripheral portion76 is sealed against the entrance of excessive undesired air byconventional and continuous sealing means 69 and 71. Similarly, thelow-vacuum space 70 between the lower platform surface 80 and the upperturntable surface 82 is sealed by conventional and continuous sealingmeans 73 and 75. Air exhaust pipes 84 and 86 (FIG. 3) lead toconventional low-vacuum and high-vacuum pumps (not shown) respectively.

Mounted on and extending downward through the upper walls of the housing66 and 68 are two conventional electron guns 88 and 90 which when inoperation project electron beams 92 downward. The electron beams 92(FIG. 4) are converged to a focus 94 by an annular focussing wire coil96 and directed to various locations of impact by a positioning wirecoil 98. The electron beam 92 from the gun 88 plays upon the powderedmolybdenum or tungsten component of the alloy, whereas the electron beam92 from the gun 90 plays upon the powdered ruthenium component,converting them to vapors which deposit themselves on the seals 14. Eachcomponent is placed in the cavity 100 of a crucible 102 of carbon orother suitable material. These powdered components are indicated by thereference letters "M" and "R" in FIGS. 3 and 4. The positioning coil 98moves the focus 94 of the converging beam 92 from place to place overthe coating material in the cavity 100 of the crucible 102 while thelatter is maintained at a negative potential and the ferrous metalmagnetic workholder 56 is maintained at a positive potential, asexplained more fully below in connection with the operation of theinvention. In this manner, the upper surfaces 20 of the seals 14 arecoated with an alloy of molybdenum-ruthenium MO₅ Ru₃ ortungsten-ruthenium W₃ Ru₂.

Immediately beyond the electron beam guns 88 and 90 in a clockwisedirection and separated from them by the sixth dwell station is a laserbeam unit 101 including a gas-tight housing 103 supplied with carbondioxide gas through a pipe 105 and containing a laser 107 emitting alaser beam 109 adapted to play upon and scan each seal 14 in each workholder 56 as it passes beneath the laser 107. The laser 107 requires apower input of 15 to 20 kilowatts to produce the laser beam 109, whichis focussed in a small spot rather than in a point upon the workpieces56 through the intermediate arrangement of a Cassegrainian opticalsystem 111 consisting of a fixed convex mirror 113 combined with amovable annular concave scanning mirror 115 mounted, for example, upongimbals (not shown) and driven to sweep the focal spot back and forthlengthwise of the seals 14 in successively parallel paths so as tointensely heat the wear-resistant coating 18 of each seal momentarily asthe laser beam 109 passes over it. The result is an interaction betweenthe wear-resistant coating layer 18 and the base layer adjacent theupper surface 20 of the base 16 so that the particles of material passacross the intervening surface boundary and interengage one another withan interlocking effect. This interlocking effect prevents the peelingoff of the freshly deposited wear-resistant layer 18 and secures itpermanently to the base 16. Such laser beam installations areconventional and well known in the optical and welding arts and theirdetails form no part of the present invention. The laser beam treatmentjust described also tends to close up pores which have occurred in thesurface layer 18 as a further preventive measure for the avoidance ofthe base metal from the base 16 emerging through such pores and smearingover the surface of the engine housing described below in connectionwith FIG. 6.

About two-thirds of a revolution in a clockwise direction from theloading station 60 is a conveyor station 104 from which the coated seals14 are conveyed from each workholder 56 to a series of stations 106,108, 110, 112, 114, 116 arranged in succession. At station 106, thecoated seals 14 are subjected to a precautionary acid bath of aqua regiaor other acid sufficient to eat away and hollow out the base metal 16wherever a portion thereof might be exposed as in a pocket, pore orother opening in the coating layer 18. If such an exposed portion of thebase metal 16 is permitted to remain on substantially the same level asthe coated metal 18, the base metal, during operation of the seal, tendsto smear over the coating metal of the above-mentioned engine housingand quickly cause the seal to fail, as has occurred in previous sealscoated with titanium carbide.

Station 108 is not an active operating station, but provides thenecessary dwell time for the effective action of the acid in hollowingout the base metal 16 below the pore or other undesired minute openingin the coating layer 18. The third station 110 is a rinse stationwherein the acid is removed from the seal by passing it through a waterdip bath. The fourth station 112 is a drying oven through which therinsed seals are then passed for removing all liquids from the surfacesthereof. The fifth station 114 is a final honing station whereat theseals are subjected to a fine honing action which gives their surfacecoating a high polish which enhances their bearing qualities. The sixthstation 116 is an unloading station at which the processed seals areremoved from the chain of processing stations.

In the method of making the seals 14, a multiplicity of bases 16 aremounted on their respective magnetized work holders 56, with the bottomsurfaces 30 of their legs 32 held against the work holder surface 58.The turntable 52 (FIG. 3) is then rotated step-by-step to station 2where a sensing device (not shown) assures the operator that the seals14 are correctly loaded on their respective work holders 56. The furtherrotation of the turntable 52 to station 3 provides for a dwell or idleperiod thereat. When the workpiece 56 rotates to station 4, it hasentered the outer or low vacuum chamber 70 and at the next step itreaches station 5 where it enters the electron gun chamber. There theupper surfaces 20 are subjected to the molybdenum-ruthenium ortungsten-ruthenium deposition brought about by the operation of the twoelectron guns 88 and 90. The former vaporizes the powdered molybdenum ortungsten in its respective crucible 102, while the latter similarlyvaporizes the powdered ruthenium in the latter's crucible 102, asindicated by the letter M in the crucible cavity 100 of FIG. 4.

The mixed vapors of the molybdenum or tungsten and ruthenium depositthemselves as alloys of these elements on the top surfaces 20 of thebases 16. The proper proportions of the two coating elements areachieved by operating the electron guns 88 and 90 for proportionateperiods of time. Thus, for molybdenum-ruthenium coating the molybdenumand ruthenium electron guns 88 and 90 respectively are operated for timeperiods in the proportion of 48% to 42% corresponding to the formula Mo₅Ru₃.

Station 6 is an "idle" station where no action takes place except thesettling together of the components applied by the electron guns 88 and90. At the next station, however, the workpieces are subjected to theeffect of a laser beam which runs along the top layer 18 just deposited,at Station 5, and so firmly unites this layer to the adjoining topsurface 20 as to prevent scaling off the layer 18 which might otherwiseoccur.

Station 8 is another idle station wherein the layer 18 which has beenremelted by the laser beam into the top layer of the base portion 16 ispermitted to consolidate therewith. At station 9, however, theworkpieces 14 are unloaded from the turntable 52 onto the conveyor 104which carries them to the acid bath of aqua regia. There, as previouslystated, the base metal 16 beneath any pores in the wear-resistantcoating 18 is eaten away to produce a hollow beneath each pore so thatthe base metal 16 cannot, during subsequent operation of the seal 14,extrude through the pores and smear over the wear-resistant layer 18 andthus nullify the protective effect of the latter, as has previouslyoccurred with prior seals in the so-called Wankel rotary engine. Fromthe acid bath 106 the workpieces or seals 14 pass through a dwellstation 108 and thence through a water rinse station 110 for removingthe acid operation at stations 106 and 108. Beyond the rinse station110, the wet seals 14 are subjected to the heat from the drying oventhereat, so that they emerge dry. The seals 14 then pass through ahoning station 114 which imparts a high polish to their wear-resistantlayers 18, after which the seals 14 reach the unloading station 116,beyond which they are subjected to any further operations deemedadvisable but beyond the scope of the present invention.

In the so-called Wankel engine, the seals 14 of the present inventionare mounted upon the tips of the lobes of a roughly triangular rotor(not shown) and cooperate, in sealing engagement, with the so-calledtrochoidal inner surface 120 (FIG. 6) on the periphery of the innerchamber 122 of the stator or housing 124. The inner surface 120 of thehousing 124 is provided with a coating 126 of the same alloy as has beendescribed above as constituting the wear-resistant layer 18 of the seals14. The coating depositing machine, generally designated 130, forapplying the wear-resistant coating 126 to the inner surfaces 120 of anassembly 128 of a multiplicity of such stators or housings 124 is shownin FIGS. 5 and 6. The housings 124 of the assembly 128 are drilled inparallel alignment to receive aligning dowels 129. The machine 130 isprovided with an elongated base 132 (FIG. 5) having an upper surface 133from one end of which rises a stationary end wall 134, preferablyintegral with the base 132 and with it constituting a frame 136. Aconduit 135 leading to a vacuum pump (not shown) is connected to a port137 in the wall 134. The base 132 near its end opposite the stationaryend wall 134 is provided with a guide surface 138 upon which is slidablymounted a movable end wall 140, the bottom surface 142 of which slidesalong the guide surface 138.

Connected as at 144 to each of the opposite sides 146 of the movable endwall 140 is the headed outer end 148 of a piston 150, the piston head(not shown) of which is reciprocable in an elongated cylinder 152pivotally mounted on a U-shaped coupling 154 which is pivotallyconnected by a headed pivot shaft 156 to a bracket 158 projectinglaterally from the fixed end wall 134. The combination of elements 148to 158 constitute a pair of pivoted hydraulic or pneumatic reciprocatoryclamping motors, generally designated 160, mounted on opposite sides ofthe fixed and movable end walls 134 and 140 for lightly clamping a stackof the engine housings or stators 124 in face-to-face engagement withone another. It will be understood that the opposite end surfaces 162 ofeach stator or housing 124 are machined to a satisfactory degree offlatness and that suitable gaskets (not shown) are inserted betweenadjacent abutting end surfaces 162 to inhibit leakage therebetweenduring the operation of the machine 130, as described below.

Mounted on the fixed and movable end walls 134 and 140 are high tensionelectrical insulators 164 and 166 which are provided with parallel bores168 (FIG. 6). The bores 168 are of a sufficient size for the temporarypassage of guide tubes 170 for the wires 172 to be subsequently explodedin the chamber 122 in a manner described below. The guide tubes 170, astheir name indicates, are for the purpose of inserting the wires 172from end to end of the machine 130, a procedure which would be difficultif not practically impossible without the use of such guide tubes.

The wires 172 are of the same wear-resistant material as employed incoating the seals 14, namely molybdenum-ruthenium or tungsten-rutheniumalloys, except that where the molybdenum-ruthenium alloy is used for theseals 14, the tungsten-ruthenium alloy is used for the housing 124.After the wires 172 have been inserted in the machine 130 by the use ofthe tubes 170, the tubes 170 are withdrawn and the openings around themin the insulators 154 and 156 are plugged so as to be air-tight,whereupon the ends of the wires 172 at one end of the machine 130 areshort-circuited by being joined to one another by a bridging conductor174 (FIG. 7). The unconnected ends of the wires 172 at the opposite endof the machine 130 are joined by conductors 176 and 178 to the oppositeterminals 180 and 182 respectively of the individual capacitors orcondensers 184, multiples of which are arranged in a capacitor orcondenser bank, generally designated 186.

In the operation of the machine 130, with the wires 172 arranged andconnected as described above, and with the assembly 125 of the enginestators or housings 124 aligned with one another along the upper surface133 of the base 132, and sealed as described above, the fluid pressureclamping motors 160 are supplied with hydraulic or pneumatic pressurefluid from a suitable pump (not shown) in the right-hand ends of theircylinders 152, whereupon the clamping pistons 150 are forced to the leftin FIG. 5, thereby tightly urging the end surfaces 162 of the individualmotor stators or housings 124 into air-tight sealed engagement with oneanother. The vacuum pump (not shown) is then started in operation towithdraw air from the aligned engine stators or housings 124. The base132 of the machine 130 is placed at a positive electrical potential,thereby also placing the engine housings or stators 124 likewise at apositive potential, whereas the wires 172 are placed at a negativepotential relatively to the capacitor bank 186. The latter is meanwhilecharged with high tension static electricity from a suitableconventional electrostatic electrical generator (not shown) unit itscharge reaches the desired power of 15 to 20 kilowatts. The discharge ofthis accumulated high tension electricity is then brought about by theclosing of a suitable electrostatic switch (not shown), whereupon theresultant surge of high-powered electrostatic electricity through thewires 172 explodes these wires and vaporizes the alloy of which they arecomposed. Such exploded wire techniques are described, for example, inthe treatise "Exploding Wires", Volume 2, edited by William G. Chace andHoward K. Moore, published by the Plenum Press, New York, N. Y., 1962.

With the explosion of the wires 172, their conversion into vapor fillsthe chambers 122 of the engine housings or stators 124 and coats theirinner surfaces 120 with a layer 126 of the above-describedwear-resistant alloy. The flow of pressure fluid through the hydraulicor pneumatic cylinders 152 is then reversed so as to cause the pistons150 thereof to move the movable end wall 140 outward away from the fixedor stationary end wall 134, whereupon the individual engine housings orstators 124 are removed from the assembly 125 thereof. The result isthat the internal surface 120 of each engine housing or stator 124 isthereby provided with a wear-resistant coating which also extends overthe projections 127 which extend toward one another from the trochoidalinner surface 120 of the stator or housing 124. Thus, when thetriangular rotor (not shown), equipped with the seals 14 at the outerends of its three lobes, engages the trochoidal inner surface 120including the projections 127, the wear-resistant nature of thesecoatings imparts to the engine a tightly-sealed combustion chamber 122,the tightness of which is of much greater duration and long life thanthe existing sealing arrangements which have been so unsatisfactory inthe rotary engine of the Wankel type.

The modified bar seal coating machine, generally designated 200, showndiagrammatically in FIG. 8 adapts the exploding-wire principle of FIGS.5 and 6 for coating the seals 14 of FIGS. 1 and 2 with the same alloys,instead of depositing the coating by means of the electron gun and lasermachine 50 of FIGS. 3 and 4. The modified machine 200 employs aturntable 202 with circumferentially-spaced workpiece recesses 204depressed below its upper surface 206 in a manner similar to theturntable 52 with its recesses or magnetic work holders 56 (FIGS. 3 and4). Stationarily mounted above the turntable 202 with an interveningspace 208 therebetween is an exploding wire coating unit, generallydesignated 210, having a hat-shaped housing 212 including a dome portion214 rising from a horizontal annular flange or platform 216 disposedabove the space 208. Continuous annular outer and inner sealing members218 and 220 are disposed between the platform 216 and the upper surface206 of the turntable 202. The opposite sides of the dome portion 214 arebored in alignment to receive tubular electrical insulators 222 and 224adapted to slidably receive a guide tube 226 which is removable to theright in FIG. 8 when the alloy wire 228 to be exploded has been passedthrough both insulators 222 and 224 as described more fully below. Thesealing members 218 and 220 define a low-vacuum space 230 therebetweenwhile the dome portion 214 defines a high-vacuum space 232, these spacesbeing connected to low-vacuum and to high-vacuum pumps respectively.

In the operation of the modified bar seal coating machine 200 of FIG. 8,let it be assumed that uncoated workpieces 14 have been placed in theholders 204 of the turntable 202 and that an alloy wire 228 similar tothe wires 172 of FIGS. 5 and 6 has been passed through the insulators222 and 224 with the aid of the guide tube 226, that the guide tube 226has then been withdrawn and the openings between the wire 228 and thebores of the insulators 222 and 224 are plugged. Let it also be assumedthat the turntable 202 has been placed at a positive electricalpotential, thereby also placing the bar seals or other workpieces 14likewise at a positive potential, while at the same time the wire 228 isplaced at a negative potential relatively to a capacitor bank (notshown) similar to the capacitor bank 186 of FIG. 7 and similarlyconnected thereto. Let it finally be assumed that conventionallow-vacuum and high-vacuum pumps (not shown) have been connected to thelow-vacuum and high-vacuum spaces 230 and 232 respectively and startedin operation to evacuate said spaces 230 and 232.

The capacitor bank is then charged with high tension static electricityas described above in connection with the machine 130 of FIGS. 5, 6 and7, and then discharged through the alloy wire 228. Thereupon theresultant surge of high-tension static electricity explodes the wire 228and vaporizes the alloy of which it is composed, as also explained abovein connection with the operation of the machine 130. This vapor,spreading throughout the space 232 and downward upon the workpieces 14,deposits thereon wear-resistant coatings 18 of molybdenum-ruthenium ortungsten-ruthenium alloy. The turntable 202 is then rotated to align thenext workholder 204 with the housing 214, whereupon a new length ofalloy wire 228 is threaded through the insulators 222 and 224 with theaid of the guide tube 226 and the above-described procedure is thenrepeated.

I claim:
 1. A method of producing a composite machine element having ametallic base member with a wear-resisting coating thereon, said methodcomprisingplacing said base member in an air-tight chamber in a firstposition, placing in said chamber a first alloy component consisting ofruthenium, placing in said chamber separately from said first alloycomponent a second alloy component consisting of a material selectedfrom the group consisting of molybdenum and tungsten, evacuating saidchamber, simultaneously evaporating each of said alloy components, anddepositing said evaporated alloy components together upon said basemember in coating alloy-forming relationship with one another and inadhering relationship with said base member.
 2. A method, according toclaim 1, wherein said evaporating of said alloy components comprisesbombarding the separate components of said alloy in said first chambersimultaneously with separate streams of electrons.
 3. A method,according to claim 1, including transferring the thus-coated elementwithin said chamber to a second position, and thereafter projecting uponthe thus alloy-coated base member a laser beam of sufficient intensityto additionally melt the thus-formed alloy coating into interfusingengagement with said base member.
 4. A method, according to claim 1,wherein said selected material is molybdenum and wherein said particlesof ruthenium and molybdenum thereby combine to form the alloy coatinghaving the composition Mo₅ Ru₃.
 5. A method, according to claim 1,wherein said selected material is tungsten and wherein said particles ofruthenium and tungsten thereby combine to form the alloy coating havingthe composition W₃ R².